tPA Variant tPA-S481A prevents impairment of cerebral autoregulation during hypotension and histopathology after TBI William M. Armstead, John Riley, Serge Yarovoi, Douglas B. Cines, Douglas H. Smith, and Abd Al-Roof Higazi Departments of Anesthesiology and Critical Care, Pharmacology, Pathology, and Neurosurgery University of Pennsylvania
Freeman, Udomphorn, Armstead, Fisk, Vavilala Anesthesiology 108: 588-595, 2008. Impairment of autoregulation correlates with GCS Impaired Cerebral Autoregulation MAP or CPP CBF (ml/100g/min) Intact Cerebral Autoregulation MAP or CPP CBF (ml/100g/min)
Cerebral autoregulation (ARI) is more impaired after moderate-severe TBI in children < 4 years. Glasgow outcome score (6 month GOS) is worse after moderate-severe TBI in children < 4 yrs. Freeman, Udomphorn, Armstead, Fisk, Vavilala Anesthesiology 108: 588-595, 20008 0.001 23 3 ARI > 0 (intact autoregulation) 5 8 ARI = 0 (absent autoregulation) 0.65 ± 0.31 0.33 ± 0.32 Mean ARI p Age ≥ 4 ( 12 ± 3) years (n=27) Age < 4 (2 ± 1) years (n=11) Table 2: 0.005 17 3 Age > 4 years 6 7 Age < 4 years p 6 month GOS > 4 (n=23) 6 month GOS < 4 (n=10) Table 4:
Plasminogen activators, NMDA, and outcome in TBI <ul><li>Glutamate release after TBI contributes to impaired cerebral hemodynamics and histopathology. </li></ul><ul><li>Tissue plasminogen activator (tPA) enhances excitotoxic neuronal cell death through interactions with NMDA receptors. </li></ul><ul><li>tPA upregulation post TBI contributes to impaired cerebral hemodynamics, histopathology, and aggravation of NMDA-mediated impairment of cerebral hemodynamics, including disturbed autoregulation during hypotension. </li></ul>
tPA contributes to impaired NMDA cerebrovasodilation through activation of JNK and ERK MAPK. Neurologic Res, in press. Impaired NMDA receptor mediated cerebrovasodilation contributes to disturbed autoregulation during hypotension after TBI. Develop Brain Res 139: 19-28, 2002.
Purpose <ul><li>tPA-S481A is a catalytically inactive tPA variant with single mutation in the active site that maintains its docking site and capacity to bind to the NMDA receptor, but cannot cleave/activate the receptor. This study investigated the ability of tPA-S481A to prevent dysregulation and histopathology after TBI. </li></ul>Hypothesis Generation of a mutant tPA that competes with wild type tPA for binding to NMDA receptors and protects it from cleavage/activation by wild type tPA will improve outcome after TBI. In the context of the neurovascular unit, impaired cerebral hemodyanamics contributes to outcome.
General Methodology <ul><li>Combined physiologic, biochemical, pharmacologic approach towards study of cerebral hemodynamics in piglet model. </li></ul><ul><li>CBF determined by microspheres, TCD, DCS </li></ul><ul><li>Immunohistochemistry. histopathology </li></ul>Advantages of the piglet model 1-5 day old pig ≈ 1-2 yr old child gyrencephalic brain more white than grey matter selective vulnerability of white matter
FPI produces pial artery vasoconstriction, which was Blocked by tPA-S481A (1 mg/kg iv) 30 min post injury Pial artery dilation during hypotension blunted after FPI, but tPA-S481A prevented such impairment.
FPI was associated with marked neuronal cell loss in CA1 and CA3 hippocampus, which was prevented by tPA-S481A
Conclusions <ul><li>These data indicate that tPA-S481A prevents impairment of cerebral autoregulation during hypotension and histopathology after FPI via its ability to bind but not activate the NMDA receptor. </li></ul><ul><li>Use of this tPA variant is a novel approach towards limiting toxicity of NMDA receptor activation associated with the robust increase in tPA and glutamate within the brain after TBI. </li></ul><ul><li>Funding: RO1 NS53410, RO1 HD57355 </li></ul>